Many types of exposure frame counters are used in photographic cameras. These counters range from simple mechanical rotating disks where frame numbers appear in a window or pass by a pointer, to digital electronic counters where frame numbers are advanced through expensive electronic components.
As shown in U.S. Pat. No. 4,687,311, a simple rotating disk is used to count the exposures used in a One Time Use Camera. In this system, every time the film in the camera is wound to the next frame, the frame counter increments one count by rotating a counter wheel. The advantages to this system are the simplicity of the counter and the independence for the need of a power source, i.e. a battery. One drawback of this system is that the frame numbers on the wheel tend to be small because the wheel needs to be small and that only every third number is printed on the wheel to save space. Intermediate numbers are omitted and substituted with dots to indicate the frame count.
As shown in U.S. Pat. No. 5,809,351, two rotating disks are used for counting the exposure frames. In this version one wheel counts the single digits for each frame and the second wheel counts the 10's of digits. This system creates a smaller counter with larger numbers.
As shown in U.S. Pat. No. 4,012,828, a Digital Frame Counter is described where the exposures used for a camera are displayed in a digital format. Such a digital frame counter could be a Liquid Crystal Display (LCD). The advantages of this type of display are that individual numbers can be larger than the above discussed rotating wheel, and each frame number can be displayed without resorting to the used of dots as intermediate frame numbers. The disadvantages of this type of display are that LCD's are relatively expensive, require support electronics and can appear dark in low light situations due to their dependence on polarizing filters for them to function.
The closest prior art is U.S. Pat. No. 5,784,189, a Micro-shutter patent assigned to MIT, that employs electrostatic fields to form micro-shutters. However, there is no suggestion for making micro-shutters operative within magnetic embodiment which is less expensive that the electrostatic environment.
From the above discussion, it should be apparent that there remains a need in the art for a display that does not require expensive electronics to operate, counts every exposure frame number and has large exposure frame numbers.